During the course of irradiating murine subjects in a modulated 2450-MHz microwave field, it was observed that dosing rates of energy just above the threshold of sensory detection or 5-X greater (2 and 10 mW/g, respectively) were associated with rises of colonic temperature that paralleled those engendered by near-threshold (and 2-X threshold) electrical shocks to the feet. Radiation and footshock in combination were additive with respect to the amplitude of the evoked thermal response. Anesthetized animals exhibited little thermal reaction to either or both classes of stimulation. The evoked thermal response thus shares with the electroencephalogram (EEG) the capability of indexing emotional arousal and CNS reactivity to "novel" stimuli.